The food and beverage industries as well as other industries such as the perfume, cosmetic and health care industries routinely use terpenes and/or terpenoid products, including for use as flavors and fragrances. However, factors such as: (i) the availability and high price of the plant raw material; (ii) the relatively low terpene content in plant; and (iii) the tedious and inefficient extraction processes to produce sufficient quantities of terpene products on an industrial scale all have stimulated research on the biosynthesis of terpenes using plant-independent systems. Consequently, effort has been expended in developing technologies to engineer microorganisms for converting renewable resources such as glucose into terpenoid products. By comparison with traditional methods, microorganisms have the advantage of fast growth without the need for land to sustain development.
There are two major biosynthetic routes for the essential isoprenoid precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), the mevalonate (MVA) pathway and the methylerythritol phosphate (MEP) pathway. The MVA pathway is found in most eukaryotes, archaea and a few eubacteria. The MEP pathway is found in eubacteria, the chloroplasts of plants, cyanobacteria, algae and apicomplexan parasites. E. coli and other Gram-negative bacteria utilize the MEP pathway to synthesize IPP and DMAPP metabolic precursors. While the MEP pathway provides a theoretically better stoichiometric yield over the MVA pathway, the MEP pathway in E. coli and in other bacteria has a variety of intrinsic regulation mechanisms that control and/or limit carbon flux through the pathway. See, Zhao et al., Methylerythritol Phosphate Pathway of Isoprenoid Biosynthesis, Annu Rev. Biochem. 2013; 82:497-530; Ajikumar P K, et al., Isoprenoid pathway optimization for Taxol precursor overproduction in Escherichia coli. Science 2010; 330-70-74.
Microbial strains and methods for improving carbon flux through the MEP pathway and through recombinant downstream terpene and terpenoid synthesis pathways are needed for industrial-scale production of terpenes and terpenoids in bacterial systems.